Fluid power braking and steering system

ABSTRACT

The vehicle hydraulic system comprises a pump, an accumulator adapted to energize a closed-centre power brake booster, and a open-centre power steering mechanism, the supply line of the power steering mechanism including a throttle in parallel relationship with a control valve. The valve member of the said control valve is actuated by a stepped piston responsive to the fluid pressures in the accumulator and in the supply line downstream said throttle, both pressures acting against a spring, thereby insuring a minimum level of pressure in the accumulator.

United States Patent 1 1 1111 3,795,393 Tanguy 1 Jan. 15, 1974 [5 FLUIDPOWER BRAKiNG AND STEERING 3,692,039 9/1972 liwuld Cl 111. 137/1111SYSTEM 3,575,192 4/1971 MacDuft' 137/118 X 3,703,186 11 1972 Brewer137/118 x [75] lnventor: Christian Tanguy, Frepillon, France [73]Assignee: Societe Anonyme 1D.B.A. Primary Examiner-Robert G. Nilson [22]Filed y 2 1972 Assistant Examiner-Edward Look Att0rneyKen C. Decker etal. [21] Appl. No.: 249,596

' 57 ABSTRACT Foreign Application Priority Data Ma 7 1971 France 7116534The vehicle'hydraulic system comprlses a pump, an y accumulator adaptedto energize a closed-centre [52] U S U 137/110 60/84 60/418 power brakebooster, and a open-centre power steer- {37/1 ing mechanism, the supplyline of the power steering [51] Int Cl Gosd 11/00 mechanism including athrottle in parallel relationship [58] Fie'ld "l'37/11O with a controlvalve. The valve member of the said 6O/4l8 2 C 2 control valve isactuated by a stepped piston responsive to the fluid pressures in theaccumulator and in [56] References Cited the supply line downstream saidthrottle, both pressures acting against a spring, thereby insuring amini- UNITED STATES PATENTS mum level of pressure in the accumulator.2,846,850 8/1958 Hall 137/118 X 2,799,996 7/1957 Van Meter 137/118 X 2Claims, 1 Drawing Figure a; 055.0 /5 054 rss 24 2 I DEV/CE F 7 -20 55 604 43 5 I z g 10 T .i} I i 1 n 63 //1iw 72 14 fifie 19E V/CE FlLlUlllDPOWER BRAKING AND STEERING SYSTEM The invention relates essentially to ahydraulic system by means of which an open-centre receiver device and apressure fluid accumulator capable of cooperating with a closed-centredevice can be supplied simultaneously from a single fluid pressuresource.

A hydraulic system already proposed comprises a pressure fluid sourcesupplying both an accumulator and, by Way of a first throttle, anopen-centre receiver device, a bypass duct connected in parallel withthe first throttle, and a control valve designed to control the passageof the pressure fluid into the bypass, so that the open-centre receiverdevice has priority in respect of the supply. A hydraulic circuit ofthis type can be used on a vehicle having a brake-assisting servo motorsupplied by the accumulator and a servo steering valve defining theopen-centre receiver device. In such an arrangement the servo steeringvalve, when operated by the driver, generally has priority over theaccumulator in respect of the supply, with the result that theaccumulator cannot be recharged. When cornering, therefore, the driverhas only a limited reserve of power for the brake-assisting servo motor.

In order to obviate this disadvantage the invention proposes a pressurefluid source supplying a pressurized fluid accumulator and anopen-centre receiver device, wherein the supply line of said receiver isprovided with a first throttle and a control valve in by-passrelationship with said throttle, said control valve comprising a valvemember actuated by piston means which are responsive to the fluidpressure in the accumulator and the fluid pressure downstream of thethrottle, both pressures acting against resilient means, thereby openingsaid control valve when the sum of the corresponding pressure forcesreaches a predetermined value.

According to another feature of the invention, the control valvecomprises a body in whose stepped bore the piston means are slidablymounted, the latter being stepped so as to define in the bore a firstchamber con nected to the accumulator and a second chamber connected toa place downstream of the first throttle.

It will be readily appreciated that the value for the fluid pressure inthe accumulator when the bypass opens, hereinafter termed the openingpressure, depends on the fluid pressure prevailing in the second chamberimmediately before opening of the bypass.

ln particular, when the driver operates the servo steering valve, theeffective fluid passage cross-section in this valve is restricted. Thepressure therefore rises in the circuit supplying the servo steeringvalve, especially in the second chamber, enabling the bypass to beopened. The more fully the servo steering valve is operated, of course,the lower is the opening pressurewhen the bypass comes into operation.The dimensions across the piston means in order to permit communicationbetween the inlet orifice and the said second chamber, the said passageincluding a cylindrical bore of which one end slides in a fluid-tightmanner on a pro- 5 jection secured to the body and the other endcooperof the various components are selected so that when ates with avalve seat on the body to define therewith the said valve meanscontrolling the flow of fluid from the inlet port to said secondchamber.

With such characteristics, of course, the dimensions of the controlvalve can be considerably reduced. It will also be noted that in orderto prevent the pressure of the fluid in the passage from reacting on thepiston means, we have provided a projection attached to the body andcapable of absorbing this reaction.

Further features of the invention will be apparent from the ensuingdescription, referring to the accompanying drawings, in which the singleFIGURE is a diagram of a vehicle hydraulic system embodying theinvention, the control valve of which being shown in longitudinalsection.

As the FIGURE shows, the hydraulic circuit of the vehicle has ahydraulic pump 2 with a substantially constant delivery, defining afluid pressure source and drawing fluid along a duct 4 from a reservoir6. The delivery side of the pump 2 is connected to the reservoir 6 by aduct 8 containing a discharge valve 10, which is calibrated for apredetermined maximum pressure so that fluid can be discharged if excesspressure threatens to damage the system.

The pump 2 supplies ducts l2, 14 leading respectively to a closed-centredevice 16 and to an opencentre receiver device 18. The closed-centredevice 16 is a brake-assisting servo motor of any conventional type inwhich the power is supplied by pressure fluid contained in anaccumulator. The open-centre receiver device 18 is a servo steeringvalve by way of example, such as disclosed in the U.S. Pat. No.3,145,626. The outlets of the closed-centre device 116 and of theopencentre device 18 are connected by respective ducts 20, 22 to thereservoir 6 (shown in two parts in the drawing for conveniences sake).

The duct 12 supplying the closed-centre device 16 contains a non-returnvalve 24, downstream of which it is joined by a connecting duct 26 to ahydraulic pressure fluid accumulator 28. The duct 14 supplying theopen-centre receiver device 18 contains a first throttle 30 and acontrol valve 32, connected in parallel with the first throttle 30 bymeans of ducts 34 and 36 connected respectively to places upstream anddownstream of the throttle 30. The duct 36 contains a second throttle 40which has a larger effective crosssection than the first throttle 30. Aduct 38 connects the control valve 32 to the accumulator 28.

The control valve 32, shown in section in the FIG- URE, comprises a body42 with a stepped bore 44, in which a piston 46 is slidably mounted. Thelatter is stepped so as to define a first chamber 48 and a secondchamber inside the bore 44. The first chamber 48 communicates by way ofa control orifice 49 with the duct 38, and the second chamber 50communicates by way of an outlet orifice 51 with the duct 36.

A plug 52 fixed to the body 42 co-operates with the piston 46 to definea cavity 54 in the bore 44. This cavity 54 communicates with atmospherethrough a passage in the plug 52.

The duct 34 is connected by an inlet orifice 55 to an annular groove 56in the wall of the stepped bore 44.

A passage 58 in the piston 46 comprises a duct 60 connecting the annulargroove 56 to a cylindrical bore 62. One end of this cylindrical bore 62slides in a fluid-tight manner on a projection 64 integral with the plug52, and the other end leads into the second chamber 50. As the FIGUREshows, that portion 66 of the piston 46 which contains the end of thecylindrical bore 62 leading into the second chamber 50 bears on a seatconsisting of a ball 68 set in the end wall of the stepped bore 44, dueto the effect of a helical spring 70 compressed between the plug 52 andthe piston 46. The piston portion 66 and ball 68 therefore define valvemeans 72.

The circuit described above operates as follows.

Assuming that the accumulator 28 is discharged, that the driver is notactuating the servo steering valve 18 and that the bypass formed by thecontrol valve 32 is closed, the pump 2 delivers fluid along the duct 14in the direction of the servo steering valve 18. The pressure thereforerises upstream of the throttle 30 so that the accumulator 28 can becharged. The characteristics of the pump 2 and the effective fluidpassage crosssection of the throttle 30 are such that the accumulator 28can be charged with pressure fluid to a value well above the minimumvalue set by the designer, so that the brake-assisting system can beused with complete safety.

During this accumulator charging period, the fluid pressures upstream ofthe throttle 30, in particular in the accumulator 28 and in the firstchamber 48, are substantially equal, The fluid pressure downstream ofthe throttle 30, in particular in the second chamber 50, is distinctlylower than the pressure upstream of the throttle 30 and is substantiallyconstant.

When the fluid pressure in the accumulator 28 reaches a predeterminedlevel, hereinafter termed the maximum opening pressure, the force actingon the piston 46, which is the resultant of the forces exerted by therespective fluid pressures in the chambers 48 and 50, is greater thanthe reacting force of the spring 70. The piston 46 is then urged towardsthe left in the FlG- URE. The piston portion 66 is moved slightly offthe ball 68, permitting a small flow of fluid through the passage 58.

Fluid then flows along the duct 36 and through the second throttle 40.The latter produces a head loss, which gives rise to a pressure rise inthe second chamber 50. This increase in pressure acts on the piston 46,which moves further to the left and opens the passage 58 fully.

Clearly, this prevents the overheating of the fluid which would resultfrom its passage through the small opening of the passage 58.Overheating is also prevented by providing the throttle 40 in the duct36 with a substantially larger effective passage cross-section than thethrottle 30.

The bypass formed by the duct 34, inlet orifice 55, annular groove 56,passage 58, second chamber 50, outlet orifice 51 and duct 36 thereforecomes into operation, and the entire delivery of the pump 2 supplies theservo steering valve 18. The fluid pressure in the circuit has droppedto an intermediate level on opening of the bypass, and the non-returnvalve 24 maintains the fluid pressure in the accumulator 28. Since thepiston 46 responds to pressure variations in the duct 34, the projection64 has been provided to absorb the pressures reacting on the piston.

Assuming that the accumulator 28 is now charged and the servo steeringvalve 18 has still not been actuated, operation of the brake-assistingservo motor 16 by the driver causes a drop in the fluid pressure in theaccumulator 28 and in the pressure in the first chamber 48. The piston46 therefore moves towards the right of the FIGURE, closing the passage58 when the fluid pressure in the accumulator 28 reaches a predeterminedlevel, termed the closing pressure.

This closing pressure is lower than the maximum opening pressure, sincethe intermediate pressure prevailing in the second chamber 50 beforeclosing of the passage 58 is greater than the pressure prevailing inthis chamber when the passage is closed. The pressure therefore risesupstream of the throttle 30, and the accumulator charging cycledescribed above is then repeated.

If the bypass is operating, the driver may operate both the servosteering valve 18 and the brake-assisting servo motor 16 simultaneously.This produces a pressure drop in the accumulator 28 and in the firstchamber 48 and a pressure rise in the bypass circuit, particularly thesecond chamber 50. The pressure charge is the greater, the more fullythe servo steering valve 18 is operated. As the piston 46 is subjectedto the sum of the forces resulting from the pressures prevailing in thechambers 48 and 50, closing of the bypass takes place when the closingpressure in the accumulator is appreciably lower than the maximumclosing pressure. The

dimensions of the control valve 32 are, of course, such that the closingpressure value is greater than the minimum pressure selected by thedesigner, so that the vehicle can be used in complete safety. When theclosing pressure is reached in the first chamber 48, the force acting onthe piston 46, which results from the effects of the pressures in thechambers 48 and 50, is smaller than the returning force of the spring,and the piston 46 is urged towards the right in the FIGURE, permittingclosure of the passage 58. The accumulator 28 now has priority inrespect of the supply, instead of the servo steering valve 18.

If the servo steering valve 18 is actuated during the accumulatorcharging cycle, the effective passage cross-section in the valve 18 isrestricted. This causes a pressure rise in the servo steering valvesupply circuit downstream of the pump 2, and in particular an increasein the fluid pressure in the second chamber 50.

The accumulator charging cycle continues. When the force which acts onthe piston 46, and which is the resultant of the effects of theresponsive pressures in the chambers 48 and 50, becomes greater than thereturning force of the spring 68, the bypass opens, the accumulatorcharging cycle ends, and the servo steering valve 18 is suppliedinstead.

I claim:

1. In a hydraulic system including a fluid pressure source, a fluidaccumulator pressurized by said source, and an open center receiverdevice operated by said source:

a first throttle in the supply line communicating the pressure sourcewith said open center receiver;

a control valve in bypass relationship with said first throttle,

said control valve including a body defining a stepped bore therewithin,stepped piston means slidably mounted in said bore and cooperating withthe latter to define first and second chambers therewithin, a firstinlet communicating one of the chambers to said supply line upstream ofsaid first orifice, a second inlet communicating the other chamber withthe accumulator, an outlet communicating said bore to saidsupply linedownstream of said first throttle, passage means extending through saidpiston for communicating said first inlet with said outlet, normallyclosed valve elements in said bore controlling communication throughsaid outlet, resilient means yieldably urging said piston to a positionclosing said valve elements, the pressure level in said chambersopposing said resilient means whereby the valve elements are opened whenthe sum of the corresponding pressure forces in said chambers reaches apredetermined value,

said passage means including a cylindrical bore in said piston parallelto said stepped bore; and

a projection secured to the body and extending into said stepped bore,one end of said cylindrical bore in said piston sealingly receiving saidpiston 2. In a hydraulic system includinga fluid pressure source, afluid accumulator pressurized by said source,

and an open center receiver device operated by said source:

a first throttle in the supply line communicating the pressure sourcewith said open center receiver,

a control valve in bypass relationship with said first throttle havingan inlet and an outlet,

said control valve including valve members controlling communicationthrough the outlet, piston means for actuating said valve members, saidpiston means being responsive to the fluid pressure in the accumulatorand the fluid pressure level upstream of the first throttle, resilientmeans opposing the fluid pressures acting on said piston means, wherebysaid resilient means urges said piston means to a position closing saidvalve elements when the sum of the fluid pressures acting on the pistonmeans drops below a predetermined level, and

a second throttle having a larger effective cross sectional area thanthat of the first throttle in the supply line communicating the outletof the control valve and a port downstream of said first throttle.

1. In a hydraulic system including a fluid pressure source, a fluidaccumulator pressurized by said source, and an open center receiverdevice operated by said source: a first throttle in the supply linecommunicating the pressure source with said open center receiver; acontrol valve in bypass relationship with said first throttle, saidcontrol valve including a body defining a stepped bore therewithin,stepped piston means slidably mounted in said bore and cooperating withthe latter to define first and second chambers therewithin, a firstinlet communicating one of the chambers to said supply line upstream ofsaid first orifice, a second inlet communicating the other chamber withthe accumulator, an outlet communicating said bore to said supply linedownstream of said first throttle, passage means extending through saidpiston for communicating said first inlet with said outlet, normallyclosed valve elements in said bore controlling communication throughsaid outlet, resilient means yieldably urging said piston to a positionclosing said valve elements, the pressure level in said chambersopposing said resilient means whereby the valve elements are opened whenthe sum of the corresponding pressure forces in said chambers reaches apredetermined value, said passage means including a cylindrical bore insaid piston parallel to said stepped bore; and a projection secured tothe body and extending into said stepped bore, one end of saidcylindrical bore in said piston sealingly receiving said piston.
 2. In ahydraulic system including a fluid pressure source, a fluid accumulatorpressurized by said source, and an open center receiver device operatedby said source: a first throttle in the supply line communicating thepressure source with said open center receiver, a control valve inbypass relationship with said first throttle having an inlet and anoutlet, said control valve including valve members controllingcommunication through the outlet, piston means for actuating said valvemembers, said piston means being responsive to the fluid pressure in theaccumulator and the fluid pressure level upstream of the first throttle,resilient means opposing the fluid pressures acting on said pistonmeans, whereby said resilient means urges said piston means to aposition closing said valve elements when the sum of the fluid pressuresacting on the piston means drops below a predetermined level, and asecond throttle having a larger effective cross sectional area than thatof the first throttle in the supply line communicating the outlet of thecontrol valve and a port downstream of said first throttle.